Tandem-in-space mass spectrometers

A tandem-in-space mass spectrometer consists of an ion source, a precursor ion activation device, and at least two nontrapping mass analyzers. The first mass analyzer is used to select precursor ions within a narrow m/z range. Isolated precursor ions are allowed to enter the ion activation device, for example, a gas-filled collision cell, where they dissociate. Created fragments continue on to the second mass analyzer for analysis. The second mass analyzer can either acquire a full mass fragment spectrum or be set to monitor a selected, narrow, m/z range. In principle the second mass analyzer could be followed by more ion activation devices and mass analyzers for MSn experiments. However, due to rapidly decreasing transmission and increasing experimental... 

In addition to MRM, the other scan modes available on a QqQ have occasionally been used for residue analysis as well. A precursor ion scan can be used to identify precursor ions from a product ion, and therefore to identify analytes and metabolites or impurities, which generate the same product ion, in complex matrices. For example, erythromycin B was identified in yogurt using this function. In this application, Q3 was held constant to measure a fragment ion at m/z 158, which is a typical product ion of compounds or impurities related to erythromycin A with a desosamine residue. Q1 was then scanned over an appropriate range, from which a precursor ion at m/z 718 was detected. The latter was identified as erythromycin B, which was an impurity in the erythromycin fermentation product. Constant neutral loss scan, which has rare applications for antibiotic analysis, records spectra that show all the precursor ions that have fragmented by the loss of a specific neutral mass. In this instance, both Q1 and Q3 scan together with a constant mass offset between the two quadrupoles. Both precursor ion and constant neutral loss scans can be performed only with ion beam tandem in-space mass spectrometers. 

Discuss the major differences between a tandem-in-space mass spectrometer and a tandem-in-time mass spectrometer. Include the advantages and disadvantages... 

Appropriate use of RF and DC voltages means that some ions can be selectively retained and product ions generated. Some of these ions can then be selected and their product ions generated. In this manner, a fragmentation chain can be established. The ion trap is a typical tandem-in-time mass spectrometer, in which precursor and product ions are created and analysed in the same physical space ionisation and ion analysis, on the other hand, take place at different times ( MS/MS in time )- The operation can be repeated several times, making it possible to perform MS11. Ion trap mass spectrometry thus consists of ... 

The quadrupole ion fiap (QIT) has developed into a highly successful MS/MS device [49]. It is a tandem-in-time mass spectrometer, meaning that all steps of MS/MS are performed in the same space but with a temporal sequence. A typical... 

Multiple mass analyzers exist that can perform tandem mass spectrometry. Some use a tandem-in-space configuration, such as the triple quadrupole mass analyzers illustrated (Fig.3.9). Others use a tandem-in-time configuration and include instruments such as ion-traps (ITMS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS or FTMS). A triple quadrupole mass spectrometer can only perform the tandem process once for an isolated precursor ion (e.g., MS/MS), but trapping or tandem-in-time instruments can perform repetitive tandem mass spectrometry (MS ), thus adding n 1 degrees of structural characterization and elucidation. When an ion-trap is combined with HPLC and photodiode array detection, the net result is a profiling tool that is a powerful tool for both metabolite profiling and metabolite identification. 

Tandem Mass Spectrometer An instrument capable of performing multiple mass (mjz) analyses. There are two major categories (1) tandem-in-space instruments (triple quadmpole and Q-TOF), (2) tandem-in-time instruments (QIT and FTICR). 

Common tandem-in-space instruments employ a quadrupole as the first mass analyzer, a multipole collision cell (usually hexapole) operated in RF-only mode, and then either a second quadrupole or a TOF tube as the second mass analyzer. These instruments are termed triple or tandem quadrupole and quadrupole-time-of-flight mass spectrometers. 

Trapping mass spectrometers can also be used as tandem mass spectrometers. Unlike beam-type mstruments, which are referred to as tandem in space, trapping mass spectrometers are tandem in time, meaning that ions are held in one region of space while the parent ion is selected and dissociated and the daughter ion analyzed sequentially in time. The ability to perform tandem mass spectrometry is inherent in the design of trapping mass spectrometers. Gen-... 

The types of tandem mass spectrometers capable of performing MS/MS experiments fall into two basic categories tandem in space and tandem in time. Tandem-in-space instruments have discrete mass analyzers for each stage of mass spectrometry examples include multisector, triple-quadru-pole, and hybrid instruments (instruments having mixed types of analyzers such as a magnetic sector and a quadrupole). Tandem-in-time instruments have only one mass analyzer where each stage of mass spectrometry takes place in the same analyzer but is separated in time via a sequence of events. Examples of this type of instrument include Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers and quadrupole ion traps, described in Chapter 3. 

A final type of tandem-in-space spectrometer is the TOF-TOF spectrometer, in which a TOF instrument followed by a timed ion selector separates the precursor ions. A collision cell then induces fragmentation, and the product ions are mass analyzed in the final TOF stage.Mass resolution of several thousand was reported. 

Tandcm-in-Time Spectrometers. Tandem-in-iime instruments form the ions in a certain spatial region and then at a later lime expel the unwanted ions and leave the selected ions to be dissociated and mass analyzed in the same spatial region. This process can be repeated many limes over to perform not only MS/MS experiments, but also MS/MS/MS and MS" experiments. Fourier transform ICR and quadrupole ion-trap instruments are well suited lor performing MS" cxperimenls. In principle, tandem-in-time spectrometers can perform M.S/MS experiments much more simply than tandem-in-space instruments because of the dilTiculty in providing different ion focal positions in the latter. Although tandem-in-time spectrometers can readily provide product ion scans, other scans, such as precursor ion scans and neui ral loss scans, are much more difficult to perform than they arc with tandem in space instruments. 

Figure 6.8 MS/MS experiments based on analysis using two spatially separate mass analyzers or tandem mass spectrometers ( tandem in space ). A collision cell is set between two mass analyzers. (Reproduced from de Hoffmann with permission from John Wiley and Sons copyright 1996.)...

Tandem-in-Space Spectrometers. In tandem-in-space instruments, two independent mass analyzers are used in two different regions in space. The triple quadrupole mass spectrometer is the most common of these instruments. In commercial triple quadrupole instruments, such as the instrument illustrated in Figure 20-2,3, the sample is introduced into a soft ionization source, such as a Cl or FAB source. The ions are then accelerated into quadrupole 1 (Q), which is an ordinary quadrupole mass filter. The selected fast-moving ions pass into quadrupole 2 (q), which is a collision chamber where dissociation of the ions selected by quadrupole 1 occurs. This quadrupole is operated in a radio-frequency-only mode in which no dc voltage is applied across the rods. This mode basically traps the precursor and product ions in a relatively high concentration of collision gas so that CAD can occur. Quadrupole 3 (Q) then allows mass analysis of the product ions formed in the collision cell. The configuration is known as the QqQ configuration. 

In tandem MS using quadrupole or magnetic sector instruments, the various steps take place in different locations in the beam path of the instrument (Yost, 1983). The term tandem-in-space (R. Yost) has been coined to show how they differ from ion storage mass spectrometers (Figure 2.234). In the ion trap analyser, a typical... 

These are not the only types of tandem mass spectrometers. There are numerous configurations of instruments that are based on the type of ion separation and many new terms associated with these instrument types. For example, there are instruments known as ion traps. The ion trap is a device that can measure mass, fragment a selected mass (as could be done in a collision cell) and then measure the mass of the fragment. The product ion produced by this all in one device is the same product ion that would be produced in a tandem quadrupole instrument. However, there is only one mass analyzer that functions as both the collision cell and mass measuring device. These types of instruments are sometimes referred to as tandem mass spectrometers, but are not abbreviated as MS/MS. The MS/MS analysis is done by separating the analysis in time (tandem in time) rather than two devices separated in space. A more generic term is best suited. This term is MS , where the n represents... 

Basically, a tandem mass spectrometer can be conceived in two ways performing tandem mass spectrometry in space by the coupling of two physically distinct instruments, or in time by performing an appropriate sequence of events in an ion storage device. Thus there are two main categories of instruments that allow tandem mass spectrometry experiments tandem mass spectrometers in space or in time. 

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